Over 1.2 million new and recurrent heart attacks are diagnosed in the US every year. More than 500,000 of these patients will die within a year and, of these, about half will die within 1 hour of the appearance of symptoms. While emergency medical technicians, paramedics, and emergency room physicians could begin treating cardiac arrhythmias that are diagnosed in the first, “golden” hour following a heart attack, most people ignore symptoms for more than 2 hours and many delay treatment for more than 12 hours.
Lateral flow immunoassay (LFIA) is a point-of-care diagnostic platform, also known as immuno-chromatography or a dipstick assay. In LFIA, an analyte is absorbed through a membrane strip typically made of nitrocellulose, is labeled with recognition elements, e.g., immuno-labeled nanoparticles, and binds to immobilized anti-analyte lines sprayed on the strip. LFIAs are commercially available for various cardiac biomarkers, e.g., INSTANT-VIEW™ and NANO-CHECK™, and the reported limit of detection is on the order of 0.1 ng/ml for cardiac troponin-I (cTnI), 20 ng/ml for myoglobin (Myo), 2 nM/ml for creatine kinase MB (CK-MB), and 0.035 pg/ml for erythropoietin (EPO).
However, LFIA has a few disadvantages. For example, LIFA is not amenable to quantitative, precise, continuous, high-throughput analysis. When continuous (or periodic), quantitative diagnostic monitoring is desired for prognosis of heart problems, alternative means of detection may be needed.
Another platform is enzyme-linked immunosorbant assay (ELISA) where antibodies to cardiac biomarkers are immobilized microliter wells, and antibody-biomarker binding event translates to a detectable fluorescence signal. Although quantitative, conventional ELISA suffers from relatively long analysis time and high consumption of samples and reagents. Microfluidic immunoassay devices have emerged to address some of these issues. Today, commercial ELISA kits, e.g., those available from Abnova Corporation and Oxis International, Inc., are available for cardiac biomarkers, and the detectable range is on the order of 1-75 ng/ml for cTnI, 5-1000 ng/ml for Myo, 0.1-100 μg/ml for C-reactive protein (CRP), and 2.5-200 ng/ml for CK-MB.
What is needed in the art, therefore, is a platform that can provide rapid, point-of-care such as analysis of blood samples that overcomes the size and power limitations of conventional platforms where a large number of sensors are required for parallel processing. An accurate, portable and fast biomarker diagnostic would facilitate field diagnoses and would also allow on-the-spot detection of coronary disease during routine clinical visits.